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I always thought processor's FSB was the limit of how fast the RAM could be. However, while configuring a Lenovo laptop, I see options for RAM that's faster than the CPU's FSB

CPU = Intel® Core™ i5-560M Processor (2.66GHz, 3MB L3, 1066MHz FSB)

RAM = 8 GB PC3-10600 DDR3 SDRAM 1333MHz SODIMM Memory (2 DIMM)

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3 Answers 3

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In short, no, some benchmarks may reveal a small advantage, but its nothing you would notice in the real world.

http://www.overclock.net/intel-memory/129552-ram-faster-than-fsb-better-performance.html

This answer does not include overclocking the cpu fsb, which is another subject all together.

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Running your memory at 1333MHz instead of 1066MHz you will likely not see any difference. All the system will do is use a divider to work out the memory speed compared to the base clock of the CPU. (I don't think the base clock of your CPU is 1066MHz, it will be 2.66GHz divided by the multiplier). Both CPU and memory frequencies are calculated using the base clock. The manufacturer may have installed 1333MHz instead of 1066MHz simply because it was cheaper.

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Back in the day the FSB speed did limit RAM speed. In that kind of setup the RAM is said to be "chained" to the FSB. These days most chipsets allow RAM to be "unchained".

In your particular case there will be a performance increase from 1066MHz to 1333MHz, but it is unlikely that you will notice it.

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Also known unchained is AKA asynchronous in the context of FSB: en.wikipedia.org/wiki/Front-side_bus –  AaronLS May 17 '12 at 23:10

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